storage/flash_map: Add flash_area_flatten

Add equivalent of flash_erase, from Flash API, to Flash Map API;
idea is the same: function tries to erase area if driver provides
erase function, otherwise writes erase_value across the defined
area.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>

include/zephyr/storage/flash_map.h

@@ -187,6 +187,29 @@ int flash_area_write(const struct flash_area *fa, off_t off, const void *src,
  */
 int flash_area_erase(const struct flash_area *fa, off_t off, size_t len);
 
+/**
+ * @brief Erase flash area or fill with erase-value
+ *
+ * On program-erase devices this function behaves exactly like flash_area_erase.
+ * On RAM non-volatile device it will call erase, if driver provides such
+ * callback, or will fill given range with erase-value defined by driver.
+ * This function should be only used by code that has not been written
+ * to directly support devices that do not require erase and rely on
+ * device being erased prior to some operations.
+ * Note that emulated erase, on devices that do not require, is done
+ * via write, which affects endurance of device.
+ *
+ * @see flash_area_erase()
+ * @see flash_flatten()
+ *
+ * @param[in] fa  Flash area
+ * @param[in] off Offset relative from beginning of flash area.
+ * @param[in] len Number of bytes to be erase
+ *
+ * @return  0 on success, negative errno code on fail.
+ */
+int flash_area_flatten(const struct flash_area *fa, off_t off, size_t len);
+
 /**
  * @brief Get write block size of the flash area
  *

subsys/storage/flash_map/flash_map.c

@@ -82,6 +82,15 @@ int flash_area_erase(const struct flash_area *fa, off_t off, size_t len)
 	return flash_erase(fa->fa_dev, fa->fa_off + off, len);
 }
 
+int flash_area_flatten(const struct flash_area *fa, off_t off, size_t len)
+{
+	if (!is_in_flash_area_bounds(fa, off, len)) {
+		return -EINVAL;
+	}
+
+	return flash_flatten(fa->fa_dev, fa->fa_off + off, len);
+}
+
 uint32_t flash_area_align(const struct flash_area *fa)
 {
 	return flash_get_write_block_size(fa->fa_dev);

tests/subsys/storage/flash_map/src/main.c

@@ -202,4 +202,65 @@ ZTEST(flash_map, test_fixed_partition_node_macros)
 		DEVICE_DT_GET(DT_MTD_FROM_FIXED_PARTITION(SLOT1_PARTITION_NODE)));
 }
 
+ZTEST(flash_map, test_flash_area_erase_and_flatten)
+{
+	int i;
+	bool erased = true;
+	int rc;
+	const struct flash_area *fa;
+	const struct device *flash_dev;
+
+	rc = flash_area_open(SLOT1_PARTITION_ID, &fa);
+	zassert_true(rc == 0, "flash_area_open() fail");
+
+	/* First erase the area so it's ready for use. */
+	flash_dev = flash_area_get_device(fa);
+
+	rc = flash_erase(flash_dev, fa->fa_off, fa->fa_size);
+	zassert_true(rc == 0, "flash area erase fail");
+
+	rc = flash_fill(flash_dev, 0xaa, fa->fa_off, fa->fa_size);
+	zassert_true(rc == 0, "flash device fill fail");
+
+	rc = flash_area_erase(fa, 0, fa->fa_size);
+	zassert_true(rc == 0, "flash area erase fail");
+
+	/* we work under assumption that flash_fill is working and tested */
+	for (i = 0; erased && i < fa->fa_size; ++i) {
+		uint8_t buf[32];
+		int chunk = MIN(sizeof(buf), fa->fa_size - i);
+
+		rc = flash_read(flash_dev, i, buf, chunk);
+		zassert_equal(rc, 0, "Unexpected read fail");
+		for (int ii = 0; ii < chunk; ++ii, ++i) {
+			if (buf[ii] != flash_area_erased_val(fa)) {
+				erased = false;
+				break;
+			}
+		}
+	}
+	zassert_true(erased, "Erase failed at index %d", i);
+
+	rc = flash_fill(flash_dev, 0xaa, fa->fa_off, fa->fa_size);
+	zassert_true(rc == 0, "flash device fill fail");
+
+	rc = flash_area_flatten(fa, 0, fa->fa_size);
+
+	erased = true;
+	for (i = 0; erased && i < fa->fa_size; ++i) {
+		uint8_t buf[32];
+		int chunk = MIN(sizeof(buf), fa->fa_size - i);
+
+		rc = flash_read(flash_dev, i, buf, chunk);
+		zassert_equal(rc, 0, "Unexpected read fail");
+		for (int ii = 0; ii < chunk; ++ii, ++i) {
+			if (buf[ii] != flash_area_erased_val(fa)) {
+				erased = false;
+				break;
+			}
+		}
+	}
+	zassert_true(erased, "Flatten/Erase failed at index %d", i);
+}
+
 ZTEST_SUITE(flash_map, NULL, NULL, NULL, NULL, NULL);